Certain drugs or medicaments (those terms being used interchangeably herein) are preferably provided in powder or dry form (e.g., lyophilized form). Such powdered drugs are commonly suspended in a liquid diluent or carrier to allow delivery to an individual through injection. The powder drug is combined with the diluent prior to injection and administered in solution form. Drug delivery systems typically have a reservoir with a large diameter, for example a syringe barrel or drug cartridge, for containing the drug solution.
Prior art devices have been developed that provide a diluent and dry substance in separate chambers of a common container or reservoir, with the container being configured to permit the flow of the diluent to the dry substance to cause mixing thereof in forming a solution. For example, U.S. Pat. No. 4,874,381 to Vetter is directed to an injector configured for mixing, while U.S. Pat. No. 4,968,299 to Ahlstrand et al. is directed to a drug cartridge for mixing.
However, due to differences in density of solids and liquids in a solid/liquid suspension, the relative velocities of the two suspension constituents may be different, thus leading to possible separation of the solid particles out of solution. Further, certain drugs are capable of being mixed and then stored for a period of time. During the storage period, solids may have a tendency to separate out of the liquid carrier. Separation of the solids from the liquid is problematic for many reasons, for example, the separation may result in delivery of an insufficient or excessive dose of the drug to the individual. Further, when solids become separated from the liquid, gravitational forces may drive the solids towards the lower end of the reservoir (typically, the patient end), which is proximal to the opening of the needle cannula or other dispensing apertures. This collection of solids proximal to the needle opening or dispensing aperture is undesirable, as it may cause clogging of the needle opening.